Internal combustion engines are expected to satisfy increasingly stringent requirements in terms of their performance and efficiency. At the same time emissions must also be kept low in order to comply with exacting statutory regulations. Requirements of this kind can be satisfactorily met if fuel is injected in a combustion chamber of the internal combustion engine in at least two operating modes and there is the possibility of switching between said operating modes. In addition to affecting the raw emissions of hydrocarbons and nitrogen oxides as well as the temperature profile of the exhaust gas, this switchover capability also has an impact on the irregular running of the internal combustion engine.
In internal combustion engines fuel can be injected into the combustion chamber of the internal combustion engine in, for example, a homogeneous mode of operation or in a stratified mode of operation.
In the homogeneous operating mode the fuel is injected into the combustion chamber of the internal combustion engine mainly during the induction phase, and consequently is still largely swirled until the fuel ignites, thus leading to a largely homogeneous fuel/air mixture. The homogeneous operating mode is preferably provided for the full-load mode of operation of the internal combustion engine.
In the stratified operating mode the fuel is introduced into the combustion chamber mainly during the compression phase. This results in a stratification of fuel in the combustion chamber at the time of ignition of the fuel. The stratified operating mode is mainly suitable for the no-load and partial-load modes of operation.
In addition to the homogeneous operating mode or the stratified operating mode there are also various intermediate forms between these two operating modes or the corresponding operating modes combined with a single injection or a multiple injection of fuel into the combustion chamber.
EP 1 199 469 A2 discloses a method for controlling an internal combustion engine, comprising fuel nozzles by means of which fuel can be injected directly into combustion chambers of the internal combustion engine. In a first step of the method for controlling the internal combustion engine the latter is initially operated in a homogeneous operating mode with single injection. The ignition angle is varied over a specific period of time in such a way that the torque decreases. At a predefined time the operating mode changes from the homogeneous operating mode with single injection to a stratified operating mode with multiple injection. During the switch from the homogeneous operating mode with single injection to the stratified operating mode with multiple injection the ignition angle is changed abruptly such that the transition from one operating mode to the other operating mode takes place in torque-neutral fashion. The control operation can also be performed in the reverse direction, i.e. such that in the stratified operating mode with multiple injection the ignition angle is initially varied while changing the torque until a point is reached at which a switch can be made from the stratified operating mode with multiple injection to the homogeneous operating mode with single injection. During the switch from the stratified operating mode with multiple injection to the homogeneous operating mode with single injection the ignition angle is changed abruptly such that no change in torque occurs.